This invention provides a process for cracking heavy hydrocarbons to form light oils and for producing hydrogen. More particularly, the invention relates to a process wherein both steam and heavy hydrocarbons are brought into contact with a catalyst containing iron in a reduced state, to thereby produce hydrogen, cracked gases, and cracked light oils, and then burning the coke deposited on the catalyst to gasify and simultaneously reduce the catalyst for its regeneration.
Some of the present inventors previously proposed a process for catalytically cracking vacuum residual oil and other heavy hydrocarbons into light oils in the presence of a laterite catalyst, wherein the coke deposited on the catalyst is burnt to reduce the iron oxide in the catayst, and then the reduced catalyst is contacted with steam to produce hydrogen (see Japanese patent application (OPI) No. 47708/79--the term "OPI" as used herein means a "published unexamined Japanese patent application").
Further, methods of cracking or gasifying heavy hydrocarbons and producing hydrogen in from three to six steps are known (see, for example, Japanese Patent Publication No. 30596/75 and U.S. Pat. Nos. 3,017,250, 2,888,395 and 2,635,947). However, no method is known that is capable of achieving these reactions effectively by two steps and using a single catalyst.
We have found that if both a heavy hydrocarbon and steam are cracked in the presence of a catalyst containing iron in a reduced state, the reactions listed below proceed simultaneously: (1) cracking of the heavy hydrocarbon into a light oil and a cracked gas and coking; (2) the reaction between H.sub.2 O and iron in a reduced state to generate hydrogen, and the oxidation of that iron; and (3) the reaction between H.sub.2 O and iron sulfide (generated in the regeneration step) to generate hydrogen sulfide, and the oxidation of iron sulfide.
We have also found that the following reactions proceed simultaneously if the catalyst containing iron in an oxidized state that has deposited thereon sulfur-containing coke resulting from the catalyst cracking step is burnt with oxygen insufficient for complete combustion of the coke; (1) partial combustion of the coke; (2) reduction of the iron in an oxidized state by the coke and carbon monoxide; (3) and the reaction between gasified sulfur compounds and the reduced iron to form iron sulfide.